7b: Application of Ln in OrgSynth

Question 1

Why are Lanthanide complexes used in organic synthesis

Answer 1

As redox reagents
Oxidising agents: (Ce4+) and (Sm2+)
or as hard lewis acids

Question 2

Ce

Answer 2

Ce4+ oxidation
Ce4+ + e –> Ce3+
One electron pathways
CAN-cerium ammonium nitrate Ce (NO3)6 (NH4)2
CAS-ceriums ammonium sulphate Ce (SO4)4 (NH4)4

selective oxidation of secondary alcohols
oxidation of phenol ethers
all radical processes etc

Question 3

Sm

Answer 3

Sm2+ reduction 
Sm least stable 2+ 
One electron pathways
Kagans reagent =Sm I2 (THF)5 
produced by
Sm + I-C2H4-I --THF--> 

Barbier rxns
PICTURE

Hydrodehalogenation (C-X to C-H
reductive cyclisations
all radical processes etc

Question 4

Ce salts

Answer 4

Ce salts (CeCl3 are used w /Rli or NaBH4 to favour 1,2 over 1,4 addition
due to hard hard addition
Luche Reduction: enone/CeCl3.7H2O/NaBH4 2
PICTURE

RLi/CeCl3 
addition of R to enolisable but hindered ketones 
Picture 
via TS
Picture

Question 5

Lanthanide ions

Answer 5

Lanthanide ions are strong Lewis acids
Catalyse organic transformations by binding and polarising substrates
eg.
activating the dienophile in the DA reaction- polarises the bond leading to a rate increase
PICTURE
Ln(OTf)3 is regularly used. Care must be taken - readily produce Trifilic acid w/ water (TfOH)
- is it the metal or the acid catalysing

can be used wa chiral ligand allows assymmetric catalysis eg DA